REV.-A
AMP 1 in the
IC
is an error amplifier used to monitor the output voltage. Figure 20 shows the
constant-voltage control circuit. Pin 1 of the
IC
provides a 5 V reference output (Vref), which is applied
to the negative terminal of AMP 1.
The error amplifier adjusts its output according to the voltages applied to the positive and negative
input terminals. This has the effect of maintaining the voltage at the terminal at 5V.
Figure 2-21 shows the output from AMP 1. When the voltage at pin 4 becomes higher than that at pin
5 (over voltage), AMP 1 outputs current modulated by pulse-width modulation
(PWM) to reduce the
output voltage of the circuit.
PWM is described below.
OUTPUT
v
VREF
Pin 4
Voltage
‘r
I
R20
R 14
3. 3K
3. 3K
Figure 2-20. Constant-Voltage
Control (+5
VDC)
R 108 and C35 compensate for phase lag
-
‘be-pin’
“
Under Voltage
( Normal
v
Voltage )
L
o
Over Voltage
/
AMP 1
OUT PUT
Figure 2-21. AMP 1 Output
in the error amplifier to prevent abnormal oscillation.
2-22
To Next Page
Loading...
